The present invention relates to the field of optical measurement and especially to geodetic measurement instruments. In particular, the invention relates to a leveling apparatus for measuring a height difference between the leveling apparatus and a leveling staff; to the use of the leveling apparatus in a geodetic measurement; and to a method of optically detecting a an object's vertical position.
A leveling apparatus is a special geodetic measurement instrument for optically measuring a height difference relative to a leveling staff, and thus a height difference between the instrument and the leveling staff.
In general, the leveling apparatus comprises at least a telescope including an optical detector, an optical system for generating an image on the optical detector and a controller. The controller is configured to receive an output signal from said optical detector and to output a leveling signal representing a detected height difference based on the output signal.
In this respect the use of a leveling staff separate from the apparatus is necessary to conduct a measurement using a leveling apparatus. A scale (measure) indicating a height relative to ground is provided on a surface of the leveling staff in the direction of elongation of the leveling staff (e.g. in the form of a coded pattern).
During measurement, the leveling staff is brought in line with an optical axis of the optical system. At this stage, the optical axis of the optical system has to be arranged in a horizontal plane. After alignment, the optical system generates an image of at least a part of the scale provided on the measuring staff on the optical detector. The image is analyzed to read the scale of the leveling staff in the middle of the image. The corresponding value is output as being the height difference between the apparatus and the leveling staff.
The above method and apparatus is explained in more detail in the essay “Die neuen Digitalnivelliere DiNi 10 und DiNi20” of Wieland Feist, Klaus Gürtler, Thomas Marold and Holger Rosenkranz, published in April 1995 in volume 57, issue 2 of the journal “VR Vermessungswesen und Raumordnung”. This journal is issued by Hanns J. Meckenstock, Domagkweg 90, D-42109 Wuppertal, Germany. The content of this essay is herewith incorporated by reference.
Another leveling apparatus is known from co-pending application PCT/EP2006/009823 from the same applicant. The entire contents of this document are incorporated herein by reference.
Examples of measurement staffs and methods of analyzing an image imaging these measurement staffs are disclosed in documents DE 197 06 970 A1 and U.S. Pat. No. 5,572,009. The entire contents of the latter document are incorporated herein by reference to become part of the present disclosure.
Normally any bar code on a leveling staff can be scanned with a linear image sensor. Newer area (i.e., two-dimensional) image sensors, especially CMOS-sensors, are more circulated on the market of electronic devices and have a lot of advantages against linear image sensors in terms of e.g. cost, speed, and integrated post processing.
However, since area image sensors usually have smaller pixels they also provide a smaller line/column length which can result in a shorter segment of code which can be read.